The present invention relates to rigid golf ball-forming compositions and golf balls formed from such compositions, as well as methods for forming a portion thereof. In particular, these golf balls have a core and a cover and preferably include the rigid composition in the core.
Multi-layer golf balls contain a core, which may include one or more layers of solid material or one or more layers of solid material encompassing a fluid therein, and a cover. Optionally, an elastic winding may also be used to form a layer surrounding the center to provide certain playing characteristics. Such balls are known as xe2x80x9cwoundxe2x80x9d balls. The multi-layer golf balls discussed herein include a core and a cover. The terms xe2x80x9ccorexe2x80x9d or xe2x80x9cball core,xe2x80x9d as used herein, include a center having one or more layers and a mantle formed of one or more layers. The terms xe2x80x9ccenterxe2x80x9d or xe2x80x9cball center,xe2x80x9d as used herein, include a solid and/or fluid mass around which a mantle and a cover are disposed. The mantle is disposed between the center and the cover, typically in concentric fashion, with the cover being the outermost portion of the ball.
A variety of golf ball compositions are known and used in various methods of manufacture. Unfortunately, these compositions and methods tend to produce balls that do not consistently achieve a symmetrical core. See, for example, the discussion in U.S. Pat. No. 6,056,842, which illustrates the poor centering that occurs in conventionally formed golf balls. This co-pending application is expressly incorporated herein by reference thereto for this purpose. Multi-layer ball production has been plagued by center portions that become off-centered during the manufacture of such balls. Off-center golf balls are a hindrance to many players, particularly those able to achieve great control using a symmetrical ball. This lack of symmetry is now believed to be caused, at least in part, by the materials and methods conventionally used in forming multi-layer golf balls. Compositions typically including greater than 40 percent cis-1,4-polybutadiene isomer are often used in forming golf ball cores, or a portion thereof. Unfortunately, many cis-polybutadiene materials are fairly soft prior to crosslinking, which can lead to the off-centering problems noted above. A number of references disclosing various cis-polybutadiene materials are discussed below.
U.S. Pat. Nos. 3,896,102; 3,926,933; 4,020,007; and 4,020,008 disclose a 1,3-butadiene component and a method and catalyst for preparing trans-polybutadiene, and that it is well known that increasing content of trans-polybutadiene is more resinous and produces a more elastic, tough, crystalline, thermoplastic solid. The ""933 and ""008 patents further disclose that trans-polybutadiene is resistant to attack by ozone and other chemical agents, and is typically used in insulation, battery cases, and golf ball covers.
U.S. Pat. No. 4,020,115 discloses the preparation of homopolymers and random copolymers of butadiene with styrene and/or isoprene that include butadiene units having a low vinyl content of not over 12 percent and a trans-polybutadiene structure of from about 70 to 81 percent. These polymers are disclosed to have broad molecular weight distribution, as well as tack and green-strength desired for manufacturing tires. A variety of trans-polybutadiene and vinyl-polybutadiene materials are also disclosed with the catalysts used for the preparation thereof.
U.S. Pat. No. 4,919,434 discloses a two-piece golf ball having a solid core of more than 40% cis-1,4-polybutadiene isomer and a cover having an inner layer of 0.1 to 2 mm thickness and an outer layer of 0.1 to 1.5 mm thickness. The inner layer is a thermoplastic resin, such as an ionomer, polyester elastomer, polyamide elastomer, thermoplastic urethane elastomer, propylene-butadiene copolymer, 1,2-polybutadiene, polybutene-1, and styrene-butadiene block copolymer, either individually or in combination.
U.S. Pat. No. 4,929,678 discloses a rubber composition for golf balls including at least 40 percent by weight polybutadiene rubber with a Mooney viscosity of 45 to 90 and a cis-bond content of at least 80 percent, a co-crosslinking agent, and a peroxide. These polymers are disclosed to have a dispersity of between 4.0 to 8.0, which is a ratio of weight average molecular weight to number average molecular weight.
U.S. Pat. No. 4,931,376 discloses butadiene polymers and copolymers with another conjugated diene having at least 80 percent butadiene by weight; 60 to 98 percent trans-polybutadiene linkages; a molecular weight distribution of 1.1 to 4.0; melting temperature of 40xc2x0 C. to 130xc2x0 C.; and a content of insolubles in boiling cyclohexane of 1% or less, as well as processes for making the same. Weight average molecular weights of 30,000 to 300,000 and trans-polybutadiene contents greater than about 30 percent are preferred. These materials are disclosed for use in golf ball covers, splint or gyps material, and the like.
U.S. Pat. No. 4,955,613 discloses golf balls made from two polybutadienes, each having a Mooney viscosity below about 50 and a cis-polybutadiene isomer content of greater than about 40 percent, more preferably greater than about 90 percent, and catalysts for preparing the polybutadienes.
U.S. Pat. No. 4,971,329 discloses solid golf balls made from polybutadiene mixtures of about 99.5 to 95 weight percent cis-1,4-polybutadiene and about 0.5 to 5 weight percent vinyl-1,2-polybutadiene. The cis-polybutadiene is made by blending from about 80 percent to 100 percent by weight of cis-polybutadiene with a cis-content of 95 percent and about 0 weight percent to 20 weight percent of cis-polybutadiene with a cis-content of about 98 percent.
U.S. Pat. No. 5,553,852 discloses three-piece solid golf balls having a center core, intermediate layer, and cover. The center core is prepared with a 1,4-polybutadiene containing more than 90% cis-polybutadiene isomer for high repulsion, co-crosslinking agent(s), peroxide, and other additives.
U.S. Pat. No. 5,833,553 discloses core compositions including polybutadiene, natural rubber, metallocene catalyzed polyolefins, polyurethanes, and other thermoplastic or thermoset elastomers, and mixtures thereof having a broad molecular weight range of 50,000 to 500,000, preferably from 100,000 to 500,000. Polybutadiene with a high cis-content is noted as being preferred.
U.S. Pat. No. 5,861,465 discloses thread rubber for wound golf balls having rubber component obtained by vulcanizing rubber composition including rubber selected from natural rubber, synthetic high-cis-polyisoprene rubber, and mixtures with at least one specific diaryl disulfide, a vulcanizing agent, and an antioxidant.
U.S. Pat. No. 6,018,007 discloses the preparation of trans-polybutadiene and other polymers and copolymers having trans configuration in the conjugated diene monomer contributed units with improved catalyst systems. The resulting polymers are rubbery, except those with high trans content, and may be vulcanized by well known methods and incorporated in tires, general rubber goods, and plastics materials.
It is desirable to reduce the off-centering problem and manufacturing inconsistencies found in many conventional golf balls, although little notice has been taken of this important part of golf ball manufacture until recently. In part, many materials are difficult to work with before they have been crosslinked. The polymers typically used in the core, particularly in mantles or shells, tend to have a memory that urges the polymer back to its earlier or original shape, which necessitates rapid compression molding to crosslink the polymer as soon as the shells are formed.
There is thus a need for an improved composition and method for manufacturing golf balls that reduces or avoids the disadvantages present when using conventional materials for golf ball cores.
The invention relates to two-piece and multi-layer golf balls having a core including a material formed from polybutadiene, a crosslinking agent, and a free-radical initiator, and a cover having a plurality of dimples disposed about the core, wherein the uncrosslinked polybutadiene polymer includes an amount of polybutadiene having at least about 80 percent trans-isomer content therein and having no more than about 10 percent vinyl-isomer and wherein the uncrosslinked polybutadiene polymer has an absolute molecular weight of at least about 100,000. In one embodiment, the isomers are preferably randomly, pseudo-randomly, or block distributed along the polybutadiene polymer backbone. In one preferred embodiment, the properties of the polybutadiene materials of the invention are with respect to the unvulcanized polymer. The invention also relates to a golf ball having a core including a material formed from polybutadiene, a crosslinking agent, and a free-radical initiator, and a cover having a plurality of dimples disposed about the core, wherein the material includes an amount of polybutadiene having at least about 80 percent trans-isomer polybutadiene content therein and having no more than about 15 percent vinyl-configuration therein and wherein the material has an absolute molecular weight of at least about 200,000 and a polydispersity of no more than about 4. Preferably, the cover has at least one of a dimple coverage of greater than about 60 percent, a hardness from about 35 to 80 Shore D, or a flexural modulus of greater than about 500 psi, and wherein the golf ball has at least one of a compression from about 50 to 120 or a coefficient of restitution of greater than about 0.7.
In one embodiment, the controlled-isomer polybutadiene has less than about 5 percent vinyl-polybutadiene. In another embodiment, the controlled-isomer polybutadiene has less than about 3 percent vinyl-polybutadiene. In yet another embodiment, the controlled-isomer polybutadiene has an absolute molecular weight average of at least about 200,000. In another embodiment, the controlled-isomer polybutadiene has an absolute molecular weight average of at least about 250,000. In one embodiment, the controlled-isomer polybutadiene has a polydispersity of no more than about 4. In another embodiment, the controlled-isomer polybutadiene has a polydispersity of no greater than about 3.
In one embodiment, the core includes a center and at least one intermediate layer. In one embodiment, the controlled-isomer polybutadiene material is disposed in the center. In another embodiment, either alternatively or in addition to the above embodiment, the at least one intermediate layer is formed including the controlled-isomer polybutadiene material. In one embodiment, the controlled-isomer polybutadiene is provided in the form of regrind having a particle size of about 0.1 micrometers to 1000 micrometers. In another embodiment, the controlled-isomer polybutadiene has a substantially uniform amount of trans-isomer after polymerization.
The invention also relates to a method of forming at least a portion of a golf ball core which includes mixing a resilient polymer component, a free-radical initiator, a crosslinking agent, and a sufficient amount of the material of claim 1 to form an uncrosslinked first mixture having a rigidity as determined by a flexural modulus greater than about 3.5 MPa (xcx9c510 psi); forming the first mixture into at least two shells in a desired shape, wherein the material imparts the rigidity to the shells to maintain the desired shape until the first mixture is crosslinked, providing a center having a first geometric center; assembling the at least two shells concentrically about the center to form a first mantle layer having a second desired shape, wherein the first mantle layer and center together form the golf ball core; and applying sufficient heat and pressure to the core for a time sufficient to crosslink the first mixture in the shells, thereby curing at least a portion of the golf ball core.
In one preferred embodiment, the method further includes providing a cover having a plurality of dimples about the golf ball core. In a preferred embodiment, the sufficient rigidity is determined by a flexural modulus of at least about 7 MPa.
In another embodiment, the core is selected to have a center and at least one intermediate layer. In another embodiment, the material is formed into a portion of the core by compression molding. In a preferred embodiment, the material is formed into a plurality of shells by injection molding. In yet another embodiment, either alternatively or additionally to the previous to the core and forming embodiments above, the center is selected to include a solid or a fluid.